Many of internal combustion engine-driven vehicles, such as all terrain vehicles (ATVs, so-called buggies), tractors and recreational vehicles, provided in recent year as vehicles mainly for traveling over rough ground are equipped with a power supply unit used as a power supply for enabling a power tool, a home electric appliance or the like to be used outdoors. For example, Japanese Patent Laid-Open No. 2004-84932 discloses a vehicle equipped with such a power supply unit.
A power supply unit provided in the above-described kind of vehicle, as disclosed in Japanese Patent Laid-Open No. 2004-40876, has an AC generator driven by an internal combustion engine for driving the vehicle, and a power converter, which converts an AC output from the AC generator changing in frequency and voltage value with the change in rotational speed of the internal combustion engine into an AC output of 100 V or 200 V having a certain commercial frequency (50 or 60 Hz). As the power converter, an inverter unit having a converter for converting the AC output from the AC generator into a DC output and an inverter for converting the DC output from the converter into an AC output of a commercial frequency is ordinarily used.
An internal combustion engine-driven vehicle such as an ATV may travel over puddles or a marshland, and there is a possibility of electric leakage (short-circuit) between the power supply unit and the vehicle body, for example, when a certain portion of the vehicle is submerged in water or wetted. The power supply unit mounted in the vehicle has a wiring to which a high voltage of AC 100 V or 200 V for example is applied. Therefore, there is a risk of electric shock to a person who is touching the vehicle body when the power supply unit is operated in the state where electricity is leaking between the power supply unit and the vehicle body.
Therefore, in this kind of vehicle, it is desirable to provide a device for detecting electric leakage from the power supply unit in order to enable taking measures for prevention of electric shock when electric leakage is detected.
In an internal combustion engine-driven vehicle equipped with a power supply unit, the engine may be stopped for prevention of electric shock when electric leakage from the power supply unit is detected. If the engine is stopped without exception when electric leakage occurs, the vehicle cannot run at the time of occurrence of electric leakage. This means failure to perform the essential function of the vehicle.
However, with an internal combustion engine-driven vehicle such as an ATV or a recreational vehicle frequently driven for traveling over rough ground or mountains in particular, there is a risk of a mishap if the vehicle cannot run. Therefore, it is necessary to avoid as much as possible the occurrence of a condition in which the internal combustion engine cannot be operated.